Investigating Fibrosis Pathways in Cystic Fibrosis Related Liver Disease to Improve Clinical Detection and Management

Abstract

Cystic fibrosis (CF), one of the most common genetic conditions in the UK, is caused by a mutation of the cystic fibrosis transmembrane regulator (CFTR) gene. CF related liver disease (CFLD) affects up to 30% of the CF population and is the 3rd most common cause of death in CF. Liver fibrosis is generated in response to ongoing chronic liver injury and results in the deposition of a pathologic collagen-rich extracellular matrix (ECM). Typically, CFLD initially develops as a focal biliary fibrosis, but can progress to a multilobular cirrhosis, with disrupted hepatic cell function, portal hypertension and ultimately liver failure. For end stage CFLD a liver transplant is the only curative option available. CFTR expression has previously been identified in cholangiocytes. CFLD is thought to originate from dysfunctional cholangiocytes with altered CFTR expression, but how this promotes fibrotic ECM deposition is not understood. In other instances of liver disease, hepatic stellate cells (HSCs) are key effector cells for fibrotic matrix deposition. After liver injury, HSCs activate into proliferative myofibroblasts and migrate through the liver depositing ECM components such as type-I collagen. In CFLD, the role of HSCs and the effect of CFTR mutation on HSC function in the production of liver fibrosis is unknown. The work presented in this thesis demonstrates for the first time that HSCs have an independent role in the production of liver fibrosis in CFLD. Quiescent HSCs with knockout of CFTR demonstrate pro-fibrotic characteristics and produce pro-fibrotic markers. Activated HSCs with knockout of CFTR have increased proliferation and fibrogenesis but reduced motility, potentially accounting for the focal nature of CFLD. In vivo, a global ∆F508 mutation of CFTR caused the most severe liver fibrosis, suggesting defects in other cells, such as cholangiocytes, perpetuates the fibrotic response. Single-nuclei RNA sequencing indicated several potential mechanistic pathways for the amplified fibrotic response in CFLD. Clinically, there is no reliable test to identify patients with CF that have developed CFLD. In this thesis we propose New Diagnostic Criteria incorporating FibroScan as a reliable diagnostic tool. Nevertheless, FibroScan has limitations, particularly given the focal nature of CFLD. Therefore, newer imaging modalities are required and contrast enhanced magnetic resonance imaging to calculate the extra cellular volume of the liver appears promising. CFLD poses an important cause of both morbidity and death in a young patient population. The results presented here demonstrate that the “New Diagnostic Criteria” significantly improve CFLD detection. For the first time CFTR-null HSCs have been shown to have pro-fibrotic characteristics and potential pathways leading to HSC activation in CFLD have been identified. Improved clinical detection and better understanding of mechanistic pathways that promote liver fibrosis in CF may help identify potential therapeutic targets for CFLD.

Date of Award	1 Aug 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Andrew Jones (Supervisor), Karen Piper Hanley (Supervisor) & Varinder Athwal (Supervisor)